The invention relates to a transmitter.
Transmitters are measurement apparatuses which detect one or more physical quantities, convert them into an electrical quantity and make measured values corresponding to the physical quantities available for further display and/or processing.
Examples are pressure measurement apparatuses, filling level measurement apparatuses and flow rate measurement apparatuses. Transmitters are used in a multiplicity of branches of industry, e.g. in installations in the chemical industry, in the foodstuffs industry or in the field of water supply. Their range of application extends from simple measurement and display through to measured value generation for process automation.
A transmitter has at least one measurement sensor for detecting at least one physical quantity. The measurement sensor typically supplies a raw signal during operation. The raw signal is fed to an electronic unit which generates from the raw signal a measurement signal corresponding to a present measured value and makes it accessible for further display and/or processing.
Information, data and/or details which depend on the specific use of the transmitter and/or the place where the latter is used are generally required for generation of the present measured value. These information, data and/or details are preferably interrogated, input and/or changed on site by means of operating elements which are accessible from outside the transmitter.
In measurement and control technology, transmitters are used for example which have a measurement sensor and an electronic unit which is arranged in a housing on a printed circuit board, and which has an area on which two conductor tracks are exposed. A force exerted on an operating element which is accessible from outside the housing moves a plunger in the direction of the printed circuit board until the said plunger bears on both the conductor tracks and effects an electrically conductive connection between the two conductor tracks. The two conductor tracks form a switch which is closed by the plunger.
This arrangement affords the advantage that the operating elements are conveniently accessible from outside the housing and, at the same time, the operating information is present directly, via the switch, wherever it is required, namely in the electronic unit. The electronic unit can thus be near to the measurement sensor In order that the shortest possible line paths are present and are nevertheless addressed externally directly via the operating elements. Short line paths are advantageous insofar as the risk of interference being coupled in and the measurement result being corrupted because of this is low if there are short lines.
What is disadvantageous however, is the fact that the plunger and the two conductor tracks are exposed. There is the risk of oxidation and corrosion of these components. In addition, the ingress of moisture into the housing can lead to undesired short-circuits which the electronic unit cannot distinguish from an intentionally performed switching operation.
An object of the invention is to specify a transmitter whose operation is not impaired by ambient influences.
For this purpose, the invention consists in a transmitter having
a measurement sensor,
an electronic unit arranged in a housing on a printed circuit board,
an operating element, which can be operated from outside the housing, and
a transmitting arrangement,
which transmits a force exerted on the operating element to a switch connected to the electronic unit,
the switch being a key of a membrane keyboard arranged on the printed circuit board.
In accordance with one embodiment, the membrane keyboard is an integral part of the printed circuit board.
In accordance with one development, the membrane keyboard is arranged on an area of the printed circuit board, on which at least two conductor tracks are exposed. It has a spacer membrane, which covers the area and which has perforations at the locations at which an electrical connection can be established between two conductor tracks. Furthermore, it has a covering membrane, which is arranged on the spacer membrane and which has contact elements on inner areas which cover the perforations and face the printed circuit board.
In accordance with one embodiment, covering membrane, spacer membrane and printed circuit board form a key in the region of each perforation and a pressure exerted on the key causes the covering membrane to flex in such a way that the respective contact element effects an electrically conductive connection between the two conductor tracks.
In accordance with a further embodiment, a surface of the printed circuit board including the electronic unit and the membrane keyboard is surface-treated, in particular coated, to provide protection against moisture.
The Invention and the advantages thereof will now be explained in more detail with reference to the figures of the drawing, which illustrate an exemplary embodiment. Identical elements are provided with the same reference symbols in the figures.